Implantable cardioverter defibrillators (ICDs) have been developed that may deliver low level electrical therapy to help pace a patient's heart and, if necessary, deliver high level electrical therapy to treat ventricular fibrillation. In general, an ICD comprises a pulse generator that receives the proximal end of an elongated and flexible lead assembly. The distal end of the lead assembly carries one or more pacing electrodes and one or more coiled defibrillation electrodes. When the ICD is implanted within a patient, the lead assembly is disposed proximate the patient's heart. If a transvenous lead assembly is employed, the distal end of the lead assembly is positioned within one or more chambers of the heart (endocardial lead), on the surface of the heart (epicardial lead), or within the surrounding vasculature. If a subcutaneous lead assembly is employed, the distal end of the lead assembly is positioned adjacent the heart. The ICD is capable of identifying and distinguishing between the different types of arrhythmias to determine the proper treatment to apply. To accomplish this, the ICD utilizes the pacing electrodes, other sense electrodes, and/or the ICD's conductive canister to monitor bioelectric signals indicative of cardiac activity.
In a small percentage of cases, an undesirably high defibrillation threshold (i.e., the amount of electrical therapy required to restore a fibrillating heart to its normal rhythm) may require an implanted ICD to administer multiple defibrillating pulses before fibrillation is corrected. The defibrillation threshold is influenced by a number of factors, which may include patient anatomy, patient medication, and migration of the ICD canister and/or leads after implantation. An undesirably high defibrillation threshold is typically addressed by equipping an ICD with an auxiliary lead assembly, such as a subcutaneous defibrillation lead assembly. This may be done during the original implantation of the ICD or during a secondary operation. In either case, the auxiliary electrode assembly is physically attached to the ICD; i.e., the proximal end of the auxiliary electrode assembly is typically plugged into an unused connector port provided on the ICD. If no unused connector port exits, the surgeon may be required to make available a connector port by removing a non-vital lead assembly connected to the ICD or, if this is not possible, the surgeon may replace the entire ICD. If a second operation is required to attach an auxiliary lead assembly to a previously implanted ICD, the ICD is excavated before the auxiliary lead assembly may be physically attached thereto. ICD excavation increases the costs and risks associated with the operation.
Considering the foregoing, it should be appreciated that it would be desirable to provide a floating defibrillation lead assembly that does not require a physical connection to an implanted medical device and, therefore, may be conceivably used with an ICD (or other medical device) without connector ports and/or with a previously implanted ICD without requiring the excavation thereof. In addition, it should be appreciated that it would be desirable to provide a floating adapter that may adapt a standard auxiliary lead assembly (e.g., a subcutaneous defibrillation lead assembly) for electrical communication with the canister of an ICD without physical attachment thereto. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. As used herein, the term ICD is intended in its broadest sense and includes any implantable medical device capable of delivering defibrillation therapy to a patient's heart.